The present invention relates, in general, to the formation of seams between two opposed edges of fabric sheets, and more particularly, relates to apparatus and methods for the formation of adhesively bonded butt seams between foamed, fully cured, elastomeric, resiliently compressible and flexible sheets of material of the type used in wet suits, dry suits and the like.
Wet suits and dry suits of the type used in aquatic sports, such as wind surfing, board surfing, water skiing and scuba diving typically are fabricated from pieces of fully cured or set (no longer thermoplastic), foamed, neoprene rubber. The suits are comprised of various fabric pieces which are cut into shapes that accommodate the user""s anatomy, provide desired elongation, and produce a variety of aesthetic effects. The wet suit pieces are joined together in seams which are either stitched or adhesively bonded, or a combination of both.
When a wet suit is fabricated using a seam stitching technique, the cost of manufacturing the wet suit is reasonable since conventional fabric seaming equipment, such as overlock sewing machines, can be employed. Thus, wet suits having stitched seams are good candidates for production sewing and semi-automated fabrication.
Unfortunately, wet suits having overlock-type stitched seams inherently leak water at the seams, which is tolerable for a wet suit, in that it is contemplated that water will enter the wet suit. Water leakage, however, is unacceptable for dry suits and should be minimized for wet suits which are intended for use in relatively cool or cold water locations.
Accordingly, dry suits and wet suits which are designed for use in cold water are formed from pieces of neoprene rubber material which are adhesively bonded together in butt seams so as not to leak water at the seams. Sometimes these suits are also blind stitched to reinforce the seam, but using current adhesive bonding techniques, the glued seams typically have a strength which is at least as great as the foamed neoprene rubber itself.
Adhesively bonding or gluing together of two foamed, fully cured or vulcanized, neoprene sheets, however, is a very labor intensive process. Conventional garment-industry fabrication techniques cannot be used because the resiliently compressible neoprene pieces are very difficult to manipulate, and the vulcanized or cured neoprene requires the application and/or activation of an adhesive bonding material on the edges of the pieces to be joined together.
Wet suits and dry suits are formed from fully cured neoprene sheets which have a thickness in the range of about 1 to about 6 millimeters, and the foamed neoprene fabric is both resiliently stretchy and flexible. In some instances, pieces of different thicknesses are bonded together, and often the neoprene will have a nylon fabric facing bonded to one or both sides of the sheet.
Currently, neoprene adhesive bonding is accomplished by applying a neoprene adhesive to the edges of the sheets to be bonded together. Usually the adhesive is applied to a plurality of similarly shaped pieces that are stacked with their edges exposed so that the adhesive can be applied with a brush to the edges only. The adhesive is then allowed to dry. After the adhesive has dried, a solvent is used to reactivate the adhesive when two pieces are to be seamed together. The pieces to be joined have their adhesive-coated edges painted with solvent, and then the edges are pressed together by hand. Finally, a pair of pneumatic pliers must be used to positively press or squeeze the edges of the pieces together to uniform bonding. The pliers are pushed down into the neoprene foam adjacent and inwardly of the edges and the jaws are closed to press the abutting edges of adjacent pieces together. This is repeated along the length of the seam by using a series of side-by-side, longitudinally adjacent pinching, releasing and moving steps.
While this technique produces a strong seam, the application of solvent using a brush, pressing together of the fabric pieces by hand and pneumatic squeezing with pliers of the pieces to bonding, all are labor intensive and undesirably costly. Moreover, the pneumatic pliers clamp the pieces together in a manner which appears to result in residual stresses in the seam. Additionally, there are significant health and safety hazards to the wet suit fabricator in connection with the application of solvent and the repeated, rapid use of pneumatic pliers.
An example of a stitched and bonded seam construction suitable for use in wet suits or the like is shown in U.S. Pat. No. 4,416,027 to Perla. This seam also includes a reinforcing insert, but as will be apparent, the hand labor required to create such a seam, and therefore the cost of forming the same, is substantial.
Adhesively bonded butt seams have been formed between sheets of plastic and rubber for various other applications. In U.S. Pat. No. 3,615,994 to MacLaine, laminated sheets, which include foamed layers, are joined together in a butt seam. In the process and apparatus of the MacLaine patent, however, the two edges which are joined at the seam are not urged toward each other, but instead are merely held in registration and overlapped on the front and back sides by a reinforcing tape.
In U.S. Pat. No. 4,231,836 to Ljungqvist, et al. and U.S. Pat. No. 4,867,823 to Pizzorno apparatus and processes for joining together unvulcanized rubber strips of material of the type used in automobile tires are disclosed. In both patents, cord strips, which are comprised of fiber or metallic cords that are oriented in a predetermined direction and surrounded by unvulcanized rubber, are joined in edge-to-edge abutting relationship. The apparatus in both patents includes bevelled wheel or roller assemblies which progressively urge the two opposed cord strip pieces toward each other during formation of the seam. The cord strips are held together initially by reason of the inherent stickiness of the unvulcanized rubber, and a separate vulcanization process is required to permanently bond the sheets together.
In both Ljungqvist, et al. and Pizzorno, the sheets being joined are not resilient, but instead are deformable or capable of plastic flow. Moreover, unlike wet suit neoprene fabric which is fully cured or vulcanized, the cord strips joined by Ljungqvist, et al. and Pizzorno are unvulcanized rubber sheets (with reinforcing cords or fibers). Since the unvulcanized rubber cord strips are plastic, application of substantial pressure to the cord strips during the joining process will permanently deform the strips. Thus, in Ljungqvist, et al. grooved wheels engage the cords to urge the strips together with minimal rubber deformation. In Pizzorno the rubber sheets are urged together by wide bevelled roller elements which are skewed and have peripheral surfaces oriented parallel to the sticky top and bottom rubber sheet surfaces. Additionally, in Pizzorno a guide wing structure is provided to direct the sheets toward each other. Thus, the wide rollers engage the top, and preferably the bottom, sticky surfaces of the sheets, and urge the sheets together.
While the Ljungqvist, et al. and Pizzorno patents disclose seam forming apparatus which is suitable for moving plastic, sticky, unvulcanized, reinforced rubber cord strips together to form a butt joint, which is subsequently bonded in a separate operation by vulcanization, they do not suggest or attempt to solve the problem of forming a butt seam between resilient, compressible, flexible, vulcanized foamed fabric sheets to which adhesive must be added. The flexible and compressible nature of foamed neoprene rubber, plus the inherent need to employ an adhesive agent, makes the formation of adhesively bonded butt seams very difficult. The neoprene material must be compressed positively together proximate the edges to uniform adhesive bonding, and the entire process must be capable of semi-automation so as to be economically comparable to sewn seams such as those made by overlock-type sewing machines. In the Ljungqvist, et al. and Pizzorno patents, for example, the vulcanizing step, which is necessary for a permanent bonded seam, is not integrated in a continuous process of moving the sheets together and bonding them to form a permanent seam.
Other adhesive activation systems are known in the prior art, but they have largely been applied in lap seams with sheet stock that is not compressible. In U.S. Pat. No. 3,171,415 to Williamson, et al., for example, ultrasonic welding is used to join together the edges of cigarette paper in a lap seam. In U.S Pat. No. 3,284,257 to Soloff, et al., ultrasonic melting of thermoplastic and thermosetting materials to form a fusion joint is disclosed, and thermally activatable rubber-based adhesives are ultrasonically activated to effect bonding of nylon parts. The patent to Soloff, et al. also discloses bonding together fabrics or textiles in a lapped or accordion arrangement. In U.S. Pat. No. 3,480,492 to Hauser, nylon parts are lapped and bonded together by ultrasonic energy using a nitrocellulose adhesive or epoxy with an exothermic additive. Similarly, in U.S. Pat. No. 3,652,354 to Su, a lap seam is formed between paper sheets soaked with a metal salt complex by using ultrasonic activation, while in U.S. Pat. No. 4,747,894 to Johnston, et al., ultrasonic activation of a starch-based adhesive to form lap seams for corrugated paper board is disclosed.
The suitability of ultrasonic adhesive activation for use in bonding foamed neoprene fabric, however, has not been pursued before, perhaps because of the observed thermal sensitivity of glued neoprene. One commonly encountered problem in connection with adhesively bonded wet suits, for example, is that the bonded seams can fail when exposed to high temperatures. Surfers standing in their wet suits in front of a bonfire on a beach, for example, have reported bonded seam failures. Previous attempts to heat-weld foamed neoprene fabric sheets together have been unsuccessful since the vulcanized neoprene does not have true thermoplastic characteristics. Intense heating merely produces burning and carbonizing of the neoprene material rather than the melting associated with vinyl and other thermoplastics which are directly heat weldable.
While foamed neoprene remains as the predominant material in wet suit and dry suit construction, other vulcanized or fully cured elastomeric materials, such as HYPALON (Dupont), KRATON (Shell) and various types of foamed plastics, such as urethane, can be used. For the purpose of brevity, this application primarily will mention neoprene or foamed elastomeric sheets rather than engaging in repeated recitations of alternative materials. The invention disclosed, however, is useful in connection with these alternative materials and in certain cases, such as in the use of HYPALON, the apparatus and process of the present invention can bond either neoprene or HYPALON without modifying the apparatus which is set up for neoprene.
Accordingly, it is an object of the present invention to provide an apparatus and method for forming adhesively bonded butt seams between resiliently compressible cured, foamed elastomeric sheets which can be adapted to more conventional continuous garment forming techniques with substantial attendant cost savings.
It is another object of the present invention to provide an apparatus and method for forming adhesively bonded seams between vulcanized neoprene foam sheets which is capable of producing a seam which is very uniform and free of residual stress so as to be at least as strong as the material itself.
Another object of the present invention is to provide a method for forming an adhesively bonded butt seam between vulcanized, resiliently compressible, flexible, foamed elastomeric fabric sheets which can be accomplished in a continuous, semi-automated operation.
Still a further object of the present invention is to provide an apparatus and method for forming adhesively bonded seams between foamed neoprene sheets in which health hazards are reduced and safety is increased.
Still another object is to provide an adhesively seamed fabric member in which the seam is substantially free of residual stress and bonding is more uniform along the seam.
Still another object of the present invention is to provide an apparatus and method for forming adhesively bonded butt seams between resiliently compressible fabric sheets which produces a durable, high-strength seam, can be accomplished with relatively inexpensive equipment, requiring minimal training and maintenance, and which enables integration of a variety of adhesive activation systems with the material handling equipment.
The apparatus and process of the present invention have other objects and features of advantages which will become apparent from and/or will be set out in more detail in the accompanying drawing and following description of the Best Mode Of Carrying Out The Invention.
In one aspect of the present invention, an apparatus for forming a butt seam between opposed edges of two resiliently compressible, flexible, fully cured, foamed, elastomeric fabric pieces is provided which includes a fabric urging assembly and a transport assembly producing relative motion between the pieces to progressively urge the edges together into abutting contact along the seam. The improvement in the apparatus of the present invention is comprised, briefly, of the urging assembly, during motion of the pieces or motion of the urging assembly or both, compressing a portion of the pieces proximate and inwardly of the edges, and the urging assembly applying a lateral force in a direction toward the edges through the adjacent compressed portion of the piece to positively press the edges together while the pieces are in abutting contact.
In another aspect of the present invention, the apparatus further includes an ensonification assembly mounted proximate the fabric manipulating assembly for transmission of sufficient sonic energy to the pieces, to cause an adhesive material carried by at least one of the edges to become suitable for adhesive bonding when the edges are pressed together by the fabric manipulating assembly. In a preferred embodiment enhancement of the transfer of sonic energy to the adhesive is accomplished by applying an incremental force, hammering, the sonic energy applying head against the fabric pieces or hammering the fabric pieces against the sonic energy transducer horn. The hammering force compresses the pieces in the thickness dimension for efficient energy transfer, and it also causes lateral expansion and pressing of the opposed edges of the fabric pieces so that the force applying assembly can be used with the sonic energy generating device to form a strong adhesively bonded butt seam without a separate edge pressing or manipulation operation.
The method of forming a butt seam between opposing edges of two resiliently compressible fabric pieces of the present invention is comprised, briefly, of the steps of compressing the thickness dimension of at least one of the pieces proximate an edge thereof, and applying a lateral force to the pieces to positively press the edges into abutting contact. The present method also preferably includes the step of activating an adhesive material carried by at least one of the edges, most preferably by ensonification, to produce adhesive bonding between the edges when they are pressed together.